Embedded Transistor

ABSTRACT

An embedded transistor for an electrical device, such as a DRAM memory cell, and a method of manufacture thereof is provided. A trench is formed in a substrate and a gate dielectric and a gate electrode formed in the trench of the substrate. Source/drain regions are formed in the substrate on opposing sides of the trench. In an embodiment, one of the source/drain regions is coupled to a storage node and the other source/drain region is coupled to a bit line. In this embodiment, the gate electrode may be coupled to a word line to form a DRAM memory cell. A dielectric growth modifier may be implanted into sidewalls of the trench in order to tune the thickness of the gate dielectric.

This application is a divisional of U.S. patent application Ser. No.14/465,578, entitled “Embedded Transistor,” filed on Aug. 21, 2014,which application is a continuation-in-part of U.S. patent applicationSer. No. 13/273,012, entitled “Embedded Transistor,” filed on Oct. 13,2011, now U.S. Pat. No. 8,853,021, issued on Oct. 7, 2014, whichapplications are hereby incorporated herein by reference.

BACKGROUND

Generally, complementary metal oxide-semiconductor (CMOS) transistorsinclude a gate electrode and a gate dielectric, which are formed on asubstrate (usually a silicon semiconductor substrate). Lightly dopeddrains are formed on opposing sides of the gate electrode by implantingN-type or P-type impurities into the substrate. An oxide liner and oneor more implant masks (commonly referred to as spacers) are formedadjacent the gate electrode, and additional implants are performed tocomplete the source/drain regions. Current flowing through thesource/drain regions may then be controlled by controlling the voltagelevels applied to the gate electrode.

Reduction in the size of CMOS transistors has provided continuedimprovement in speed, performance, circuit density, and cost per unitfunction over the past few decades. As the gate length of theconventional bulk MOSFET is reduced, the source and drain increasinglyinteract with the channel and gain influence on the channel potential.Consequently, a transistor with a short gate length suffers fromproblems related to the inability of the gate to substantially controlthe on and off states of the channel.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIGS. 1-8 illustrate various intermediate stages in the manufacturing ofan embedded transistor in accordance with an embodiment;

FIG. 9 illustrates a plan view of a memory cell utilizing an embeddedtransistor in accordance with an embodiment;

FIGS. 10A and 10B are cross-sectional views of the memory cellillustrated in FIG. 9;

FIGS. 11-12 illustrate an embodiment which uses a double sided tiltangle implant in accordance with an embodiment; and

FIGS. 13-14 illustrate an embodiment which uses a single tilt angleimplant in accordance with an embodiment.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the embodiments are discussed in detail below.It should be appreciated, however, that the present disclosure providesmany applicable inventive concepts that can be embodied in a widevariety of specific contexts. The specific embodiments discussed aremerely illustrative of specific ways to make and use the disclosure, anddo not limit the scope of the disclosure. Throughout the various viewsand illustrative embodiments of the present disclosure, like referencenumbers are used to designate like elements.

Referring first to FIG. 1, a substrate 110 is provided with a firstpatterned mask 112 formed thereon. The substrate 110 may comprise anysemiconductor material and may comprise known structures including agraded layer or a buried oxide, for example. In an embodiment, thesubstrate 110 comprises bulk silicon that may be undoped or doped (e.g.,p-type, n-type, or a combination thereof). Other materials that aresuitable for semiconductor device formation may be used. In anembodiment, however, the substrate 110 is bulk silicon.

The first patterned mask 112 is formed to pattern the underlyingmaterials, such as the underlying substrate 110. In an embodiment, thefirst patterned mask 112 comprises a photoresist material that has beenmasked, exposed, and developed. Generally, the photoresist material isdeposited, irradiated (exposed) and developed to remove a portion of thephotoresist material, thereby defining a pattern as illustrated inFIG. 1. The remaining photoresist material protects the underlyingmaterial from subsequent processing steps, such as etching.

Also shown in FIG. 1 is an optional hard mask 114. The hard mask 114 isa protective layer to prevent the underlying structures, such as thesubstrate 110, from being removed during an etching process. In somesituations, a mask in addition to the first patterned mask 112 isdesirable due to the materials to be patterned, the duration of the etchprocess, the types of etchants used, and the like. In an embodiment inwhich the substrate 110 is a silicon substrate, one such suitable hardmask 114 comprises an oxide layer, such as a silicon oxide layer, and anoverlying nitride layer, such as a silicon nitride (Si₃N₄) layer. Theoxide layer may be formed by any oxidation process, such as wet or drythermal oxidation in an ambient comprising an oxide, H₂O, NO, or acombination thereof, or by chemical vapor deposition (CVD) techniquesusing tetra-ethyl-ortho-silicate (TEOS) and oxygen as a precursor. Theoxide layer may also be formed, for example, by an in-situ steamgeneration (ISSG) process in an ambient environment of O₂, H₂O, NO, acombination thereof, or the like. In an embodiment, the oxide layer isabout 50 Å to about 100 Å in thickness. The nitride layer may be formedusing CVD techniques using silane and ammonia as precursor gases. Thenitride layer may be patterned using CHF₃ plasma, and the oxide layermay be patterned using CF₄ plasma.

One of ordinary skill in the art will appreciate that other maskmaterials and/or structures may be used to form either or both of thefirst patterned mask 112 and the hard mask 114. For example, othermaterials, a single layer, three or more layers, or the like may beused. In an alternative embodiment, the hard mask may comprise a singlesilicon nitride layer without an underlying oxide layer.

FIG. 2 illustrates the substrate 110 after the substrate has beenpatterned in accordance with an embodiment. The substrate 110 may bepatterned by performing one or more etching steps, thereby formingtrenches 216 ₁-216 ₅ (collectively referred to as trenches 216) havingfins 218 interposed between adjacent ones of the trenches 216. Thesubstrate 110 may be etched by, for example, HBr/O₂, HBr/Cl₂/O₂, orSF₆/Cl₂ plasma. As will be discussed in greater detail below, the fins218 will form source/drain regions of a transistor, while alternatingones of the trenches will form the gate electrodes of the transistor.Other ones of the trenches will form an isolation structure, e.g.,shallow trench isolations (STIs).

In the embodiment illustrated in FIG. 2, the trenches 216 may have adepth D₁ (and hence the height of the fins 218) of about 1,000 Å toabout 4,000 Å, and the fins 218 may have a width W₁ of about 100 Å toabout 800 Å. While the width W₁ of the fins 218 are illustrated in thisembodiment are the same, other embodiments may utilize fins 218 ofvarying widths. As noted above, subsequent processing forms source/drainregions in the upper portions of the fins 218. Thus, the size (e.g., thewidth and height of the fins 218) may be adjusted to achieve the desiredelectrical characteristics of the transistor. Moreover, it should benoted that the fins on the same wafer may have different widths anddepths.

Additionally, a width W₂ of the trenches may also vary. As noted above,the trenches will become the gate electrodes and isolation trenches. Assuch, the width of the trenches may be adjusted to vary the gate lengthand the isolation characteristics. For example, it may be desirable insome embodiments to provide wider isolation trenches as compared to thetrenches for the gate electrode to provide greater isolationcharacteristics between adjacent devices. In other embodiments, a widertrench for the gate electrode may be desirable.

Also illustrated in FIG. 2 is the removal of the first patterned mask112 (see FIG. 1). The first patterned mask 112 may be removed, forexample, by an O₂ plasma dry strip and a mixture of concentratedsulphuric acid and hydrogen peroxide.

Referring now to FIG. 3, a first dielectric material 320 is formed overthe substrate 110, substantially filling the trenches 216. In anembodiment, the first dielectric material 320 comprises a silicon oxidelayer that may be formed by a high-density plasma CVD deposition processusing SiH₄ and O₂ mixture.

As illustrated in FIG. 3, the first dielectric material 320 isplanarized to a top surface of the substrate 110 in accordance with anembodiment. The first dielectric material 320 may be planarized, forexample, by using a chemical-mechanical polishing (CMP) process using anoxide slurry wherein the substrate 110 acts as a stop layer.

FIG. 4 illustrates removal of the first dielectric material 320 fromselect ones of the trenches 216, such as trenches 216 ₂ and 216 ₄. In anembodiment, the first dielectric material 320 may be selectively removedfrom trenches 216 ₂ and 216 ₄ by forming and patterning a mask layer(not shown) to protect the first dielectric material 320 in trenches 216₁, 216 ₃, and 216 ₅ while leaving the dielectric material in trenches216 ₂ and 216 ₄ exposed. The mask may be patterned usingphotolithography techniques similar to those discussed above withreference to etching the substrate 110 as illustrated in FIGS. 1 and 2.For example, a photoresist material may be formed, exposed according toa desired pattern (e.g., exposing trenches 216 ₂ and 216 ₄), anddeveloped. Additionally, a hard mask such as that discussed above mayalso be used.

In an embodiment in which the first dielectric material 320 is a siliconoxide and the substrate 110 is silicon, the first dielectric material320 may be removed using an anisotropic dry etch process using anetchant having a high etch selectivity between the substrate 110 and thefirst dielectric material 320, such as CF₄ or C₂F₆. In this manner,substrate 110 is relatively unaffected while etching or removing thefirst dielectric material 320.

FIG. 5 illustrates the substrate 110 after a gate insulator layer 526 isformed along the surfaces of the trenches 216 ₂ and 216 ₄ and a gateelectrode material 528 is formed within the trenches 216 ₂ and 216 ₄, inaccordance with an embodiment. Generally, the gate insulator layer 526prevents electron depletion between the source/drain regions and thegate electrode. In an embodiment, the gate insulator layer 526 comprisesan oxide layer formed by an oxidation process, such as wet or drythermal oxidation in an ambient comprising an oxide, H₂O, NO, or acombination thereof, an in-situ steam generation (ISSG) process in anambient environment of O₂, H₂O, NO, a combination thereof, or the like,or by chemical vapor deposition (CVD) techniques usingtetra-ethyl-ortho-silicate (TEOS) and oxygen as a precursor. Othermaterials including, high k dielectric materials, such as HfO₂, HfSiO₂,ZnO, ZrO₂, Ta₂O₅, Al₂O₃ and the like, and other processes, such asAtomic Layer Deposition (ALD), Atomic Vapor Deposition (AVD), and thelike, may also be used. In an embodiment, the gate insulator layer 526has a thickness between about 20 Å and about 50 Å. It should be notedthat FIG. 5 illustrates that the gate insulator layer 526 does notextend over the first dielectric material 320 for illustrative purposesonly. Whether the gate insulator layer 526 extends over the firstdielectric material 320 is dependent upon, at least in part, the methodused to form the gate insulator layer 526. For example, a thermalprocess generally results in an embodiment similar to that illustratedin FIG. 5, while the gate insulator layer 526 may extend over the firstdielectric material 320 when the gate insulator layer 526 is formedusing, e.g., a CVD process or an ISSG process.

Optionally, an implant may be performed to aid or retard the formationof the gate insulator layer 526. For example, a nitrogen implant may beperformed to retard an oxide growth in select areas, such as the bottomof the trench, and a fluorine implant may be performed to increase theoxide growth. In an embodiment, a nitrogen implant may be performed atan angle normal to the upper surface of the substrate. In thisembodiment, sidewalls of the trenches will be implanted less than thebottom surface of the trench. The nitrogen implant along the bottom ofthe trench retards the oxide growth, thereby resulting in a thinner gateinsulator layer along the bottom of the trenches as compared to thesidewalls of the trench. In another embodiment, the implant angle may beadjusted to implant nitrogen along the sidewalls, thereby resulting in athicker gate insulator along the bottom as compared to the sidewalls.Similar effects, e.g., relatively thinner or thicker gate insulatorlayer along the bottom of the trenches, may be obtained using a fluorineimplant to increase the relative growth rate of the gate insulatorlayer.

It should be noted that the substrate 110 may be doped before formingthe gate insulator layer to prepare, for example, the channel region.For example, in forming a p-type transistor having p-type dopedsource/drain regions, an n-type dopant, such as phosphorous, arsenic,nitrogen, antimony, or the like, may be implanted into the channelregion (along the sidewalls and bottom of the trenches 216 ₂ and 216 ₄)of the substrate 110 prior to forming the gate insulator layer 526.Similarly, in forming an n-type transistor having n-type dopedsource/drain regions, a p-type dopant, such as boron, aluminum, gallium,indium, or the like, may be implanted into the channel region of thesubstrate. The implant angle may be adjusted to ensure properimplantation along the sidewall regions of the trenches 216 ₂ and 216 ₄as well as the bottom of the trenches 216 ₂ and 216 ₄. Alternatively,the substrate 110 may be doped prior to forming the trenches by formingan n-well or a p-well, respectively, in which the trenches 216 ₂ and 216₄ are formed.

For example, a p-type transistor may be formed by implanting phosphorousions at an angle of about 0° to about 5° relative to the bottom surfaceof the trenches 216 ₂ and 216 ₄ and at an angle between about −25° toabout 25° relative to of a vertical sidewall of the trenches 216 ₂ and216 ₄ at a dose of about 1E12 to about 3E13 atoms/cm² and at an energyof about 20 to about 400 KeV. An n-type transistor may be formed byimplanting boron ions at an angle of about 0° to about 5° relative tothe bottom surface of the trenches 216 ₂ and 216 ₄ and at an anglebetween about −25° to about 25° relative to a vertical sidewall of thetrenches 216 ₂ and 216 ₄ at a dose of about 1E12 to about 3E13 atoms/cm²and at an energy of about 5 to about 300 KeV.

The gate electrode material 528 comprises a conductive material, such asa metal (e.g., tantalum, titanium, molybdenum, tungsten, platinum,aluminum, hafnium, ruthenium), a metal silicide (e.g., titaniumsilicide, cobalt silicide, nickel silicide, tantalum silicide), a metalnitride (e.g., titanium nitride, tantalum nitride), dopedpoly-crystalline silicon, other conductive materials, or a combinationthereof. In one example, amorphous silicon is deposited andrecrystallized to create poly-crystalline silicon (poly-silicon). In anembodiment, the gate electrode layer is formed by depositing, e.g., CVD,low-pressure CVD (LPCVD), and the like, a conformal layer covering thesubstrate 110 and filling the trenches 216 ₂ and 216 ₄. Thereafter, aplanarizing process, such as a CMP process, may be performed to removeexcess material, thereby forming a structure similar to that illustratedin FIG. 5.

The gate electrode material 528 may be deposited doped or undoped. Forexample, in an embodiment the gate electrode material 528 may be formedby depositing a polysilicon layer and, once applied, the polysilicon maybe doped with, for example, phosphorous ions (or other P-type dopants)to form a PMOS device or boron (or other N-type dopants) to form an NMOSdevice. The polysilicon may also be deposited, for example, by furnacedeposition of an in-situ doped polysilicon. Alternatively, the gateelectrode material 528 may comprise a polysilicon metal alloy or a metalgate comprising metals such as tungsten, nickel, titanium, and titaniumnitride, and the like, for example.

FIG. 6 illustrates recessing of the gate electrode material 528 (seeFIG. 5) to form the gate electrodes 630 along the bottom portions of thetrenches 216 ₂ and 216 ₄. In embodiments in which the gate electrodematerial 528 comprises polysilicon, the recessing may be performed usingeither dry or wet etching. In the case dry etching is used, the processgas may include CF₄, CHF₃, NF₃, SF₆, Br₂, HBr, Cl₂, or combinationsthereof. Diluting gases such as N₂, O₂, or Ar may optionally be used. Inthe case wet etching is used, the chemicals may include NH₄OH:H₂O₂:H₂O(APM), NH₂OH, KOH, HNO₃:NH₄F:H₂O, and/or the like. In an embodiment, thegate electrode material 528 is recessed from about 500 Å to about 2,000Å.

Referring now to FIG. 7, a second dielectric layer 732 is formed overthe substrate 110, filling the recesses above the gate electrodes 630 inthe trenches 216 ₂ and 216 ₄. The second dielectric layer 732 may beformed of similar materials using similar processes as those discussedabove with reference to the first dielectric material 320. Afterdepositing the second dielectric layer 732, a planarization process,e.g., a CMP process, may be used to remove excess material, therebyforming a structure similar to that illustrated in FIG. 7. In anembodiment, this planarization process exposes the fins 218.

FIG. 8 illustrates formation of the source/drain regions 834 inaccordance with an embodiment. The source/drain regions 834 may be dopedby implanting n-type or p-type dopants. For example, n-type transistormay be formed by implanting an n-type ion such as phosphorous ions, at adose of about 1E15 to about 5E15 atoms/cm² and at an energy of about 20to about 100 KeV. A p-type transistor may be formed by p-type ions, suchas boron ions, at a dose of about 1E15 to about 5E15 atoms/cm² and at anenergy of about 10 to about 50 KeV.

Furthermore, FIG. 8 also illustrates optional silicide regions 836 inaccordance with an embodiment. The silicide regions 836 reduce contactresistance between the source/drain regions 834 and contacts formed insubsequent processing steps. The silicide regions 836 may be formed, forexample, by depositing a metal layer (not shown) such as titanium,nickel, tungsten, or cobalt via plasma vapor deposition (PVD)procedures. An anneal procedure causes the metal layer to react with thesubstrate 110, e.g., silicon, of the source/drain regions 834 to formmetal silicide. Portions of the metal layer overlying other areas, suchas the first dielectric material 320 (e.g., the isolation structures)and second dielectric layer 732 remain unreacted. Selective removal ofthe unreacted portions of the metal layer may be accomplished, forexample, via wet etch procedures. An additional anneal cycle may be usedif desired to alter the phase of silicide regions 836, which may resultin a lower resistance.

As can be appreciated, the above paragraphs describe embodiments of anembedded transistor that may be used in a variety of applications. Forexample, FIGS. 9, 10A, and 10B illustrate an embodiment in which theembedded transistor disclosed above is utilized as an access transistorin a DRAM memory cell. In particular, FIG. 9 illustrates a plan view ofa plurality of DRAM memory cells, FIG. 10A illustrates a cross-sectionalview along the A-A′ line of FIG. 9, and FIG. 10B illustrates across-sectional view along the B-B′ line of FIG. 9. A single memory cellis designated by the dashed box 950.

The memory cell 950 includes bitline 952 formed in, for example, thefirst metallization layer M1 having bitline contacts 954 electricallycoupling the bitline 952 to one of the source/drain regions 834 of theunderlying access transistor. The other of the source/drain regions 834of the access transistor is electrically coupled to a storage node 956via storage node contacts 958. The storage node 956 may be, for example,a metal-insulator-metal (MIM) capacitor, a planar capacitor, a U-shapedcapacitor, a vertical capacitor, a horizontal capacitor, a non-capacitorstorage structure, or the like. The gate electrode 630 is electricallycoupled to a wordline (WL).

It should be appreciated that embodiments such as some of thosediscussed above utilize a single mask and etch process to form theisolation trenches and the embedded gate electrodes. In this manner,embodiments disclosed herein using a self-aligned process avoidmisalignment issues that may be seen in other approaches in which theisolation trenches and the gate electrode trenches are formed withseparate mask and etching processes. It is believed that theseembodiments reduce wordline disturbance issues.

Embodiments disclosed herein also allow layout designers greaterfreedom. For example, the gate length is defined by the depth of thetrench as opposed to the pitch between fins, thereby possibly allowingthe gate length to be adjusted without increasing the pitch.

FIG. 11 illustrates further embodiments in which the thickness of thegate insulator layer 526 (not illustrated in FIG. 11 but illustrated anddiscussed in this embodiment below with respect to FIG. 12) may be tunedalong the sidewalls of the trenches 216. In the embodiment that isinitiated in FIG. 11, the fins 218 and the trenches 216 have alreadybeen formed and some of the trenches have been filled with the firstdielectric material 320 (as described above with respect to FIGS. 1-3).Once formed, a double sided tilt angle implant that comprises a firstimplantation process (represented in FIG. 11 by the arrows labeled 1101)and a second implantation process (represented in FIG. 11 by the arrowslabeled 1103) is utilized to implant a dielectric growth modifierprimarily into the sidewalls of the trenches 216. Additionally, by usinga series of angled implantation processes, little to none of thedielectric growth modifier is implanted into the bottom of the trench216. In an embodiment the dielectric growth modifier may be a dielectricgrowth enhancer, such as fluorine or a dielectric growth inhibitor, suchas nitrogen.

In an embodiment in which the dielectric growth modifier is thedielectric growth enhancer, when the dielectric growth modifier isimplanted primarily into the sidewall of the trench 216, the gateinsulator layer 526 will grow faster along the sidewalls and form athicker gate insulator layer 526 along the sidewalls of the trench 216than along the bottom of the trench 216. Alternatively, in an embodimentin which the dielectric growth modifier is the dielectric growthinhibitor, the gate insulator layer 526 will grow slower along thesidewalls and form a thinner gate insulator layer 526 along thesidewalls of the trench 216 than along the bottom of the trench 216.

In an embodiment the first implantation process 1101 implants thedielectric growth modifier at a first angle θ₁ such that the dielectricgrowth modifier is primarily implanted into the sidewall of the trenchand shuttering effects are avoided. For example, in an embodiment inwhich the fins 218 have a spacing of the width W₂ and the trenches 216have the depth D₁, the first implantation process 1101 is performed atthe first angle θ₁ that is greater than an arctangent of the width W₂divided by the depth D₁ (e.g., θ₁>tan⁻¹ (W₂/D₁)). By using an anglegreater than the arctangent of the width W₂ divided by the depth D₁, thedielectric growth modifier will be primarily implanted into thesidewalls of the trench 216 instead of in the bottom of the trench 216.

In an embodiment in which the dielectric growth modifier is fluorine,the first implantation process 1101 may implant the fluorine and form afirst dielectric growth modifier zone 1105 within the sidewall of thetrench 216. In an example, the first dielectric growth modifier zone1105 may be formed to have a concentration of the dielectric growthmodifier (e.g., fluorine) of between about 1E13 cm² and about 1E15 cm²,such as about 1E14 cm².

Similarly, the second implantation process 1103 may be performed in anopposite direction than the first implantation process 1101 in order toimplant the dielectric growth modifier into an opposing sidewall of thetrench 216 than the first implantation process 1101. In this embodimentthe second implantation process 1103 may implant the fluorine at asecond angle θ₂ that is opposite the first angle θ₁. The second angle θ₂may similarly be based on the width W₂ and the depth D₁, such as bybeing larger than the arctangent of the width W₂ divided by the depth D₁(e.g., θ₂>tan⁻¹ (W₂/D₁)), although in an opposite direction than thefirst angle θ₁ in order to implant the dielectric growth modifier intoan opposite sidewall of the trench 216 than the first implantationprocess 1101.

The first implantation process 1101 and the second implantation process1103 may be performed as separate processes, with the substrate 110repositioned between the first implantation process 1101 and the secondimplantation process 1103. Alternatively, the first implantation process1101 and the second implantation process 1103 may be performed as asingle process, wherein the substrate 110 is rotated during the processsuch that the opposing sidewalls of the trench 216 are exposed to theimplantation process. Any suitable method of implanting the dielectricgrowth modifier may alternatively be used, and all such methods arefully intended to be included within the scope of the embodiment.

In an embodiment in which the dielectric growth modifier is fluorine,the second implantation process 1103 may implant the fluorine and form asecond dielectric growth modifier zone 1107 within the sidewall of thetrench 216. In an example, the second dielectric growth modifier zone1107 may be formed to have a concentration of the dielectric growthmodifier (e.g., fluorine) of between about 1E13 cm² and about 1E15 cm²,such as about 1E14 cm².

FIG. 12 illustrates that, once the first implantation process 1101 andthe second implantation process 1103 have been performed to form thefirst dielectric growth modifier zone 1105 and the second dielectricgrowth modifier zone 1107, the gate insulator layer 526 may be formed asdescribed above with respect to FIG. 5. For example, the gate insulatorlayer 526 may be an oxide layer formed by an oxidation process, such aswet or dry thermal oxidation in an ambient comprising an oxide, H₂O, NO,or a combination thereof, an in-situ steam generation (ISSG) process inan ambient environment of O₂, H₂O, NO, a combination thereof, or thelike, or by chemical vapor deposition (CVD) techniques usingtetra-ethyl-ortho-silicate (TEOS) and oxygen as a precursor, althoughany suitable process and material may alternatively be utilized.

However, with the presence of the first dielectric growth modifier zone1105 and the second dielectric growth modifier zone 1107 locatedprimarily in the sidewalls of the trench 216, the gate insulator layer526 will grow at a faster rate along the sidewalls of the trench 216(where there is a higher concentration of fluorine) than along thebottom of the trench 216 (where there is a lower concentration offluorine, if any at all). As such the gate insulator layer 526 will bethicker along the sidewalls of the trench 216 than along the bottom, andgradually decreases from the top of the trench 216 to the bottom of thetrench 216.

For example, in an embodiment in which the dielectric growth modifier isfluorine, the gate insulator layer 526 along a sidewall of the trench216 may have a first thickness T₁ at a top of the trench 216 of betweenabout 30 Å to about 40 Å. The gate insulator layer 526 may also have asecond thickness T₂ along the sidewall at a bottom of the trench 216 ofless than about 20 Å. In other words, the gate insulator layer 526 alongthe sidewall will have a reduction in thickness from the top of thetrench 216 to the bottom of the trench 216. The gate insulator layer 526will also have a third thickness T₃ along the bottom of the trench 216that is less than the first thickness T₁ and less than or equal to thesecond thickness T₂, such as by being less than about 20 Å.

Once the gate insulator layer 526 has been formed, the gate electrodes630 may be formed over the gate insulator layer 526, the seconddielectric layer 732 may be formed over the gate electrodes 630, thesource/drain regions 834 may be formed in the fins 218 (represented inFIG. 15 by the dashed lines labeled 834), the optional silicide regions836 (not separately illustrated in FIG. 14) may be formed, and thebitline contacts 954, the bitline 952, the storage node contacts 958 andthe storage node 956 may be formed. In an embodiment the gate electrodes630, the second dielectric layer 732, the source/drain regions 834, theoptional silicide regions 836, the bitline contacts 954 and the storagenode 956 may be formed as described above with respect to FIG. 5-10 b.However, any other suitable methods and materials may alternatively beused.

By utilizing the dielectric growth modifier, the formation of the gateinsulator layer 526 can be better controlled to produce desired results.For example, by increasing the thickness of the gate insulator layer 526along the sidewalls, the gate insulator layer 526 will have a largerequivalent oxide thickness as well as being physically thicker. As such,the gate induced drain leakage (GIDL) can be reduced and no drawback onsub-threshold leakage (Isoff) since gate insulator thickness remainsthinner at the bottom of trench 216. Additionally, using this process,there are no undesirable side effects on the channel mobility.

FIG. 13 illustrates another embodiment in which the gate insulator layer526 (not illustrated in FIG. 13 but illustrated and discussed below withrespect to FIG. 14) is formed with a decreasing thickness along asidewall of the trench 216. In this embodiment the first implantationprocess 1101 is performed as described above with respect to FIG. 11.For example, the dielectric growth modifier is implanted into a sidewallof the trench 216 to form the first dielectric growth modifier zone1105, and the implantation is performed at the first angle θ₁, whichtakes into account the width W₂ divided by the depth D₁, so as toimplant the dielectric growth modifier primarily into the sidewallinstead of along the bottom of the trench 216.

However, in this embodiment the dielectric growth modifier is implantedinto one sidewall (e.g., with the first implantation process 1101)without implanting the dielectric growth modifier into a facingsidewall. For example, in this embodiment the first implantation process1101 may be utilized to implant the dielectric growth modifier into onesidewall of the trench 216. However, instead of following the firstimplantation process 1101 with the second implantation process 1103, thesecond implantation process 1103 is not performed, and the dielectricgrowth modifier is implanted into the single sidewall of the trench 216,such that the other sidewall remains primarily free from the dielectricgrowth modifier, forming the first dielectric growth modifier zone 1105in a single sidewall of the trench 216 (and also along the top of thefins 218).

FIG. 14 illustrates that, once the first implantation process 1101 (butnot the second implantation process 1103) has been performed, the gateinsulator layer 526 may be formed as described above with respect toFIG. 5. For example, the gate insulator layer 526 may be an oxide layerformed by an oxidation process, such as wet or dry thermal oxidation inan ambient comprising an oxide, H₂O, NO, or a combination thereof, anin-situ steam generation (ISSG) process in an ambient environment of O₂,H₂O, NO, a combination thereof, or the like, or by chemical vapordeposition (CVD) techniques using tetra-ethyl-ortho-silicate (TEOS) andoxygen as a precursor, although any suitable process and material mayalternatively be utilized.

However, with the presence of the dielectric growth modifier within onesidewall of the trench 216, the gate insulator layer 526 will grow at adifferent rate (e.g., faster) rate along the sidewall of the trench 216that has been implanted with the dielectric growth modifier and not asfast along the opposing sidewall of the bottom of the trench 216. Assuch, the gate insulator layer 526 will decrease in thickness along thesidewall from the top of the trench 216 to the bottom of the trench 216.For example, at the top of the trench 216 along the sidewall that wasimplanted with the dielectric growth modifier, the gate insulator layer526 may have the first thickness T₁, while near the bottom of the trench216 the gate insulator layer 526 along the sidewall may have the secondthickness T₂. Additionally, in this embodiment the gate insulator layer526 along both the bottom of the trench 216 and the other sidewall (thesidewall that was not implanted with the dielectric growth modifier) mayhave the third thickness T₃.

Once the gate insulator layer 526 has been formed, the gate electrodes630 may be formed over the gate insulator layer 526, the seconddielectric layer 732 may be formed over the gate electrodes 630, thesource/drain regions 834 may be formed in the fins 218 (represented inFIG. 15 by the dashed lines labeled 834), the optional silicide regions836 (not separately illustrated in FIG. 14) may be formed, and thebitline contacts 954, the bitline 952, the storage node contacts 958 andthe storage node 956 may be formed. In an embodiment the gate electrodes630, the second dielectric layer 732, the source/drain regions 834, theoptional silicide regions 836, the bitline contacts 954 and the storagenode 956 may be formed as described above with respect to FIGS. 5-10 b.However, any other suitable methods and materials may alternatively beused.

By utilizing the dielectric growth modifier along one of the sidewallsof the trench 216, the formation of the gate can be better controlledsuch that a thicker dielectric may be formed on one of the source/drainregions 834 (e.g., on the source line node of the embedded transistor)without having a thicker dielectric on the other source/drain region 834(e.g., bit line node). As such, the benefits of the thicker dielectricon the source line node (e.g. GIDL reduction) may be achieved withoutdeterioration of a drive current that may occur with a thickerdielectric on the bit line node.

In accordance with an embodiment, a method of manufacturing asemiconductor device comprising implanting a dielectric growth modifierinto a first sidewall of a trench is provided. A gate insulator layer isformed along the first sidewall and a bottom of the trench, wherein thegate insulator layer forms at a different rate along the first sidewallof the trench than along the bottom of the trench such that the gateinsulator layer has a decreasing thickness along the first sidewall ofthe trench.

In accordance with another embodiment, a method of manufacturing asemiconductor device comprising implanting a first dielectric growthmodifier into a first sidewall of a trench at a first angle is provided.A second dielectric growth modifier is implanted into a second sidewallof the trench different from the first sidewall, wherein the implantingthe second dielectric growth modifier is performed at a second angledifferent from the first angle. A gate insulator layer is grown along abottom of the trench, the first sidewall, and the second sidewall,wherein the gate insulator layer has a first thickness along the bottomof the trench that is less than a second thickness along the firstsidewall and the second sidewall.

In accordance with yet another embodiment, a semiconductor devicecomprising a trench in a substrate, the trench comprising a firstsidewall, a second sidewall, and a bottom is provided. A gate insulatorlayer lines the first sidewall, the second sidewall, and the bottom ofthe trench, wherein the gate insulator layer lining the first sidewallhas a decreasing thickness from a top of the trench to the bottom of thetrench.

Although the present disclosure and its advantages have been describedin detail, it should be understood that various changes, substitutions,and alterations can be made herein without departing from the spirit andscope of the disclosure as defined by the appended claims. Moreover, thescope of the present application is not intended to be limited to theparticular embodiments of the process, machine, manufacture, andcomposition of matter, means, methods, and steps described in thespecification. As one of ordinary skill in the art will readilyappreciate from the present disclosure, processes, machines,manufacture, compositions of matter, means, methods, or steps, presentlyexisting or later to be developed, that perform substantially the samefunction or achieve substantially the same result as the correspondingembodiments described herein may be utilized according to the presentdisclosure. Accordingly, the appended claims are intended to includewithin their scope such processes, machines, manufacture, compositionsof matter, means, methods, or steps.

What is claimed is:
 1. A semiconductor device comprising: asemiconductor substrate; a plurality of trenches formed within thesemiconductor substrate, each one of the plurality of trenches having afirst height; one or more dielectric materials filling a first one ofthe plurality of trenches; a gate dielectric lining a second one of theplurality of trenches, the gate dielectric having a first thickness thatvaries along a first sidewall of the second one of the plurality oftrenches; a dielectric growth modifier located within the semiconductorsubstrate adjacent to the gate dielectric; and a gate electrode locatedwithin the second one of the plurality of trenches adjacent to the gatedielectric.
 2. The semiconductor device of claim 1, wherein the gatedielectric has a second thickness that varies along a second sidewall ofthe second one of the plurality of trenches.
 3. The semiconductor deviceof claim 1, wherein the first thickness at a top of the first one of theplurality of trenches is between about 30 Å and about 40 Å.
 4. Thesemiconductor device of claim 1, wherein the first thickness at a bottomof the first one of the plurality of trenches is less than 20 Å.
 5. Thesemiconductor device of claim 1, wherein the gate dielectric has asecond thickness that is constant along a second sidewall of the secondone of the plurality of trenches.
 6. The semiconductor device of claim5, wherein there is no dielectric growth modifier located within thesemiconductor substrate adjacent to the gate dielectric with the secondthickness.
 7. A semiconductor device comprising: a first trench with afirst depth in a semiconductor substrate, the first trench filled withone or more dielectric materials; a second trench with the first depthin the semiconductor substrate, the second trench being at leastpartially filled with a gate dielectric and a gate electrode, the gatedielectric having a first portion with a first thickness adjacent to asidewall of the second trench and a second portion with a secondthickness less than the first thickness adjacent to a bottom surface ofthe second trench; and a dielectric growth modifier within thesemiconductor substrate adjacent to either the first portion or thesecond portion.
 8. The semiconductor device of claim 7, wherein thedielectric growth modifier has a concentration of between about 1E13 cm²and about 1E15 cm².
 9. The semiconductor device of claim 7, wherein thefirst thickness is between about 30 Å and about 40 Å.
 10. Thesemiconductor device of claim 9, wherein the second thickness is lessthan 20 Å.
 11. The semiconductor device of claim 7, wherein the secondthickness is less than 20 Å.
 12. The semiconductor device of claim 7,wherein a sidewall of the second trench is free from the dielectricgrowth modifier.
 13. The semiconductor device of claim 7, wherein thegate dielectric has a third portion with a third thickness less than thefirst thickness along a bottom of the second trench.
 14. Thesemiconductor device of claim 13, wherein the third thickness is lessthan about 20 Å.
 15. A semiconductor device comprising: a trench in asubstrate, the trench comprising a first sidewall, a second sidewall,and a bottom; an isolation region in the substrate, wherein theisolation region and the trench extend into the substrate a firstdistance; and a dielectric growth modifier zone located adjacent to thetrench; and a gate insulator layer lining the first sidewall, the secondsidewall, and the bottom of the trench, wherein the gate insulator layerlining the first sidewall has a decreasing thickness from a top of thetrench to the bottom of the trench.
 16. The semiconductor device ofclaim 15, wherein the gate insulator layer lining the second sidewallhas a constant thickness.
 17. The semiconductor device of claim 15,wherein the gate insulator layer lining the second sidewall has adecreasing thickness from the top of the trench to the bottom of thetrench.
 18. The semiconductor device of claim 15, further comprising afirst concentration of a dielectric growth enhancing material locatedwithin the first sidewall.
 19. The semiconductor device of claim 18,further comprising a second concentration of the dielectric growthenhancing material located within the second sidewall.
 20. Thesemiconductor device of claim 19, wherein the bottom of the trench isprimarily free from the dielectric growth enhancing material.